1. Field
The following description relates to an OTP memory cell and a fabricating method thereof, and such as, for example, to an anti-fuse OTP memory cell and a fabricating method thereof.
2. Description of Related Art
A one-time-programmable (OTP) memory device is a type of nonvolatile memory device in which programming is possible only once on a circuit.
Various types of OTP memory devices have been developed. Among them, a unit cell of an anti-fuse OTP memory device generally includes a well formed in a semiconductor substrate, a gate insulating layer formed on the well and including at least one fuse region, a gate electrode formed on the gate insulating layer, and a junction region, such as a source region and a drain region, formed in the well.
The one-time programming is accomplished by applying a write voltage to the gate electrode, which causes the insulation state of the fuse region to be blown. Then, the fuse region of the gate insulating layer and the junction region adjacent to the fuse region act as resistors that have resistance values of a predetermined range.
However, after being blown, the fuse region may have a resistance value that exceeds a predetermined range. This corresponds to a blowing failure. To improve the yield thereof, an anti-fuse type memory device may be provided with two fuses in the unit cell. In such an anti-fuse type memory device, if any one of the two fuse regions is blown, a write voltage that is applied to the other fuse region may drop, causing a blowing failure. If the fuse region blown first results in a blowing failure, both of the fuse regions fail in blowing, causing an error during a read operation.
On the other hand, it is ideal that blowing occurs in an edge portion of the fuse region when a write voltage is applied to the gate electrode. However, in some cases, the center portion of the fuse region is blown rather than the edge portion. In such an event, after the blowing, a fuse poly (fuse region) and a lower well may form a reverse-biased diode. In such an event, the corresponding unit cell becomes a defective cell.